WHO statistics showed that Liberia bore the brunt of the latest surge in fatalities, with 53 deaths, while there were 17 in Sierra Leone and 14 in Guinea.

But in a glimmer of possible good news, Brown said eight medical workers including two doctors who had been given experimental US-made drug ZMapp were responding to the treatment.

Overall, the UN health agency has tallied 2,240 cases of confirmed, probable and suspect Ebola infection since the outbreak began early this year, making it the deadliest since the discovery of the disease in the former Zaire in the 1970s.

From Guinea, where the current outbreak began, it has spread to three other states, overwhelming inadequate public health services already battling with common deadly diseases such as malaria.

Guinea has recorded a total of 543 cases and 394 deaths, Sierra Leone 848 cases and 365 deaths and Liberia 834 cases and 466 deaths.

Nigeria, the most populous country in Africa, has 15 cases and four fatalities, according to WHO data.

Efforts to contain the spread across west Africa have run up against local distrust of outside doctors, and fears that aid workers may carry infection with them.

"At first people thought that when they got here, they were going to have all their blood removed and they would die," Nallo, being treated at an Ebola clinic this week in Sierra Leone, told AFP.

And in Monrovia, Ebola has sown panic and irrational violence.

Youths raided the medical facility in the West Point slum in Monrovia on Saturday, sending the 17 Ebola patients fleeing for their lives - and potentially spreading more of the lethal virus across the city.

'Encouraging signs' of controlBut WHO spokeswoman Fadela Chaib noted "encouraging signs" in Nigeria and Guinea, where prevention measures were starting to take effect.

"What's encouraging there is that there's been just one identified chain of transmission. That is very good news," she said.

The Nigerian outbreak has been traced to a sole foreigner, a Liberian-American who died in late July in Lagos. All subsequent Nigerian victims had had direct contact with him.

"All the measures taken by the Nigerian authorities have shown a positive impact," said Chaib, adding that Guinea was also making some halting progress.

Food aid for quarantine zonesThe last days of an Ebola victim can be horrific, with agonising muscular pain, vomiting, diarrhoea and haemorrhaging as vital organs break down.

No cure or vaccine is currently available for the disease, which is spread by close contact with body fluids, meaning patients must be isolated.

But given the extent of the crisis, the WHO has authorised largely untested treatments - including ZMapp and the Canadian-made VSV-EBOV vaccine, both barely tested drugs with unknown effects on humans.

In the absence of an effective vaccine, countries have thrown up quarantine cordons in infected areas such as Gueckedou in Guinea, Kenema and Kailahun in Sierra Leone and Foya in Liberia.

Around one million people live in the zones, Chaib said, adding that while they helped rein in transmission, residents could struggle to obtain basic needs.

"It is essential that people in those zones have access to food, water, good sanitation and other basic supplies," she added.

The WHO is working with the World Food Programme to get regular food and other non-medical supplies to the zones.

Porous borderWhile the WHO does not recommend international air travel restrictions, it has created a task force with global airline and tourism groups to try to contain the spread, and several nations in west Africa have closed their borders to affected countries.

Countries beyond Africa are also on high alert.

On Tuesday, medical authorities in Spain said a man who returned from Sierra Leone had been placed in an isolation ward after coming down with a fever.